Breathing 100% Oxygen at about 30 feet

[sytech]

I am aware that if you could take an Emergency Cylinder (for use by EMT's etc.) of 100% oxygen to breathe from to a depth of about 20 feet our so you would start to get symptoms of oxygen toxicity. At about 25-30 feet you may start to have convulsions and drown.

I was explaining this to a friend but he didn't believe. What is the actual mechanism causing the convulsions or coma and hence the drowning?:

Is it that the partial pressure (it's really not "partial" though is it?) of the oxygen at that depth is itself toxic?

Is it because the ambient pressure causes you to breath a 'denser' amount of oxygen thereby causing a convulsion or coma?

Any comments will be appreciated.

Sy

 

[scubak]

Take a look at this, may help....
http://www.divematrix.com/showthread.php?p=12286#post12286
K

 

[do it easy]

I think the short answer in my non-professional opinion, is that the oxygen in the blood produces free radicals (these are the things that antioxidants try to protect us from, although I think the drug companies give them a bad rap) which overload the nervous system and cause seizures. Essentially, too much of a good thing is bad for you

 

[spectrum]

Is it that the partial pressure (it's really not "partial" though is it?) of the oxygen at that depth is itself toxic?

It is partial pressure however in this case the partial value is greater than the normal surface atmosphere. Breathing pure O2 the surface you are being subjected to a partial pressure of 100% (as opposed to 21% in air) At 33 feet (2 ATM total) you would have a PPO2 of 200% or 2.0.

Nitrox guidelines generally seek to limit O2 exposure to 1.4 with a contingency of going to 1.6. Those limits correspond roughly with 13.2 feet and 19.8 feet for pure 02. So you can see that as you exceed 20 feet on pure O2 you are skating on thin ice.

The effect of excess exposure is usually a seizure. Do it easy's explanation is as straightforward as I've heard.

Pete

 

[ekewaka]

partial pressure
–noun Physics, Chemistry.
the pressure that a gas in a mixture of gases would exert if it occupied the same volume as the mixture at the same temperature.

In this case it is not partial pressure because 100% O₂ is not a mixture.

 

[Gene_Hobbs]

For explaining Oxygen Toxicity, the Wikipedia article on this topic is not bad and pretty easy to follow.

I do stand by my suggestion in the DiveMatrix thread mentioned above to read the Butler article(s) on operational use of O₂, from our "suggested reading list".

 

[DavidPT40]

The wikipedia article said that the oxygen can react with certain metals to attack unsaturated fats in the cell. Maybe this somehow causes certain voltage gates in the cell to open, causing nerve impulses that lead to convulsions.

 

[rawls]

CNS oxygen toxicity has a time dose relationship and the onset of symptoms is highly individualized. If you go to 33 ft breathing 100% O2, which, as spectrum stated, would equal 2ata ppO2, you would not necessarily begin to have convulsions. The acceptable limit for O2 is 1.4ata ppO2. For deco purposes it is acceptable for the ppO2 to be 1.6 ata because you are at rest. Breathing 100% at 20 ft equals 1.6ata ppO2.

 

[wilkie]

A Wikipedia article can be changed!!!This is not "burning bush" info. Either you, or I can, by loging on can change this information.....

Take a nitrox course, learn for yourself, live & enjoj diving, OK ? Don,t get "facts off of the net", Bogus info can hurt you.

 

[ekewaka]

A Wikipedia article can be changed!!!This is not "burning bush" info. Either you, or I can, by loging on can change this information.....

Take a nitrox course, learn for yourself, live & enjoj diving, OK ? Don,t get "facts off of the net", Bogus info can hurt you.

Are you suggesting that everything that is taught in a nitrox course is absolutely 100% correct?